The objective of this research proposal is a detailed understanding of the reactions catalyzed by cytochrome c peroxidase. The investigation is subdivided into areas. The first area is concerned with the question of what factors are involved in making a heme protein a good peroxidase. The reactivity of the heme site will be investigated with emphasis placed on elucidating the involvement of particular amino acids in the protein. The second area is concerned with the mechanism of electron transfer from the oxidized enzyme intermediates to oxidizable substrates, in particular the natural substrate, ferro-cytochrome c. Studies are designed to determine whether complex formation between substrate and enzyme is required for electron transfer, the possibility of multiple electron transfer pathways, the involvement of amino acid residues in the electron transfer pathway and the effect of substrate redox potential and charge.